"Attempts to restore Russia's 1991 borders will lead only to one thing - a global war with Western countries with the use of our entire strategic (nuclear) arsenal against Kyiv, Berlin, London, and Washington. And against all other beautiful historic places that have long been included in the flight targets of our nuclear triad," Medvedev said in a reference to the triad of intercontinental ballistic missiles, submarine-launched ballistic missiles, and strategic bombers with nuclear weapons.
So literally they're threatening to lob nukes if people don't stop not recognizing their attempt to just grab territory from weaker neighbors.
I don't think Russia wants that precedent in the air with China looking so hungrily at Siberia